Made some addition for my spool shelf design, endcap for those whom wooden dowel extends from shelf bracket to prevent filament spool tipping over. It should fit tightly but I also included holes for M3 wood screw just to be sure.

Also made divider so you can separate different type of filaments from each other on one shelf and not mixing them accidentaly. Divider is just clip on, no additionl hardware required.

This all fits my spool shelf here with all different dimension wooden dowels, 20mm, 23mm and as well 1inch : https://makerworld.com/en/models/88779#profileId-95016